Alastair Stuart

Question 1

Advantages of using Machining Processes

Answer 1

Produces good surface finishes.
Enables the creation of complex geometries and components.
Allows the production of components that have the required Product Performance and Assembly Fit.

Question 2

Disadvantages of using Machining Processes

Answer 2

Production of waste material
Time Consuming
Tool wear

Question 3

Dimensional Accuracy

Answer 3

How closely the final dimension of a part relates to the required dimension.

Question 4

Dimensional Tolerance

Answer 4

The permissible variation in the dimensions of a part.

Question 5

Surface Finish (Roughness)

Answer 5

The average of vertical deviations from the normal surface of a part.

Question 6

Conventional Machining Processes

Answer 6

Turning, Drilling, Milling, Broaching, Planning, Reaming, Sawing

Question 7

Abrasive Machining Process

Answer 7

Grinding, Polishing, Honing, Finishing, Abrasive Flow Machining

Question 8

Non-conventional Machining Processes

Answer 8

Laser Cutting, Water Jet Cutting, Electro Discharge Machining

Question 9

Cutting Speed, Feed, Depth

Answer 9

Cutting Speed (v) - Primary motion between tool and work piece.
Feed (f) - Motion of tool moving laterally across work piece.
Depth (d) - Depth of cut below surface of work piece.

Question 10

Cost of Cutting Tool Materials

Answer 10

HSS
HSS + Cobalt
Cemented Carbides
Cubic Boron Nitride

Question 11

Turning Conditions Equations

Answer 11

Material Removal Rate:
Rmr = vfd
Machining Time:
Tm = (πD0L)/fv

Question 12

Drilling Conditions Equations:

Answer 12

Tip Length:
A = 0.5Dtan(90-θ/2)
Machining Time:
Tm = (d+A)/f
Material Removal Rate:
Rmr = (πD^2f)/4

Question 13

Group Technology

Answer 13

Families of similar shaped parts that require similar machining are grouped together to make the machining process more efficient.

Question 14

Uses of Steel Based Cutting Tools
(Carbon Steel/ HSS/ HSS + Cobalt)

Answer 14

Cheaper
Suitable for general machining
Cobalt makes tougher tools, capable of dealing with hardened materials

Question 15

Uses of Cast Cobalt/ Cemented Carbides/ Cermets/ Ceramics

Answer 15

Mediumly Expensive
Harder so capable of dealing with more demanding machining operations.
Harder but more brittle.

Question 16

Uses of Cubic Boron Nitride (CBN)/ Diamond

Answer 16

Premium Tool
Hardest tool material
Last long if used correctly

Question 17

What is Cutting Force and Thrust Force?

Answer 17

Cuttting Force is in the direction of cutting.
Thrust force is perpendicular to the cutting force.
They can be measured using a dynamometer.

Question 18

Causes of Discontinuous Chips

Answer 18

Brittle Materials at low cutting speeds
Incorrect cutting speed, impurities, low rake angle, lack of cutting fluid.
High tool-chip Friction because of large depth of cut.
Results in irregular surface finish.

Question 19

Causes of Continuous (Stringy) Chips

Answer 19

Ductile Materials cut at high speed, with small feed and depth.
Good surface finish.
Sharp cutting edge and low tool-chip friction encourage this.

Question 20

Causes of Continuous Chips with Built-up Edge

Answer 20

Ductile Materials at low to medium cutting speeds.
Friction between tool and chip causes work material to adhere to the rake.
Damages Tools
Portion of BUE can be embedded in the workpiece.

Question 21

Cause of Serrated Chip

Answer 21

Semi continuous, saw-tooth like appearance.
Due to alternating high and low shear strain.
Occurs on difficult to machine metals: Titanium and Nickel alloys.

Question 22

What is the Purpose of Abrasive Processes?

Answer 22

Is used to achieve a high surface finish.
Mainly used on hard materials.
Very slow and costly process.

Question 23

What are the Traditional Abrasive Materials and their uses?

Answer 23

Aluminium Oxide- Steel/ Ferrous High-Strength Alloys.
Silicon Carbide - Harder but not as tough. Aluminium/ Brass/ S Steel/ Cast iron/ Ceramics

Question 24

Advantages and Disadvantages of Non-Conventional machining processes

Answer 24

+ves:
Little or no tool wear
Low clamping force required
Low levels of Heat Affected Zones
Residual Stresses
-ves:
Low material removal rates
Costly

Question 25

Laser Cutting and Machining

Answer 25

High energy beam of photons generated by LASER or an electron beam.
Gas blows molten material away from work area.

Question 26

Electro Discharge Machining (EDM)

Answer 26

Non contact process
Material removed by successive electrical discharges and dielectric carries the material away.
Spark melts and vaporises the work piece.
Material needs to be conductive but can be any hardness.

Question 27

Using Assembly Lines

Answer 27

Workers specialised on a single operation.
Allows the use of sub-assemblies and interchangeable parts.

Question 28

Arc Welding

Answer 28

A fusion welding process in which a pool of molten metal is formed near electrode tip, and as electrode moves along joint, weld pool solidifies.
Produces temperatures of 5500C
Most add a filler material to increase volume and strength of weld.
Arranged Joints are Butt/ Corner/ Lap/ Tee/ Edge

Question 29

Friction Welding

Answer 29

Generates heat by friction and combined with pressure creates joint.
No filler/ Covering gas

Question 30

Spot Welding

Answer 30

Electric current passed through a lap joint, causes heat which melts plate material. This solidifies creating a point where the plates have fused together, weld nugget.

Question 31

What are the basic features of Fusion Welded Joints?

Answer 31

Fusion Zone
Weld Interface
Heat Affected Zone (HAZ)
Unaffected base metal zone

Question 32

Power Density and Heat Affected Zones

Answer 32

Pd = P/A
Higher Pd smaller HAZ
Highest
Electron Beam Welding
Laser Welding
Plasma Welding
MIG welding
TIG welding
Lowest

Question 33

Welding Defects

Answer 33

Cracks - Fractures either in weld or in base metal adjacent to weld.
Cavities - Incomplete Fusion, Interference of atmospheric gases, or Shrinkage.
Solid Inclusions - Non-metallic material encased in weld.
Distortion - Expansion and Contraction of workpiece.